1. Field of the Invention
The present disclosure relates to an organic light emitting diode display device and, more particularly, to an organic light emitting diode display device using a support pattern and a method of fabricating the organic light emitting diode display device.
2. Discussion of the Related Art
Among various flat panel displays (FPDs), an organic light emitting diode (OLED) display device has superior properties such as high luminance and low driving voltage. The OLED display device uses an emissive electroluminescent layer to realize a high contrast ratio and a thin profile, and is excellent at displaying a moving image because of a short response time of several micro seconds (μsec). Also, the OLED display device has no limitation on a viewing angle and is stable even in a low temperature. Since the OLED display device is driven by a low voltage of about 5V to about 15V in direct current (DC), it is easy to fabricate and design a driving circuit. Moreover, since a fabrication process of the OLED display device requires only a deposition apparatus and an encapsulating apparatus, the fabrication process of the OLED display device is simple.
In general, the OLED display devices are classified into a passive matrix type and an active matrix type. In a passive matrix type OLED display device, elements of scan lines and signal lines are formed in a matrix such that the scan lines and the signal lines cross each other. In addition, since the scan lines are sequentially driven, each pixel displays an instant luminance that is the same as a product of a required luminance and the number of the scan lines.
In an active matrix type OLED display device, a thin film transistor (TFT) that is a switching element turning on/off the pixel is formed in each pixel and a voltage applied to the pixel is stored in a storage capacitor. Since the storage capacitor supplies the voltage until
a next frame, each pixel operates during a frame regardless of the number of scan lines. Since a required luminance is obtained even when a low voltage is applied, the active matrix type OLED has advantages such as low power consumption, high resolution and applicability for a large size. As a result, the active matrix type OLED display device has been widely used.
The active matrix type OLED display device includes a gate line, a data line and a power line. The gate line and the data line cross each other to define a pixel region, and the power line is parallel to and spaced apart from the data line. A switching thin film transistor (TFT), a driving TFT, a storage capacitor and a light emitting diode are formed in the pixel region. When a gate signal is applied to the gate line, the switching TFT is turned on and a data signal of the data line is supplied to a gate electrode of the driving TFT through the switching TFT. Since the driving TFT is turned on, a source voltage of the power line is supplied to the light emitting diode through the driving TFT, thereby emitting light.
When the driving TFT is turned on, a level of a current flowing through the light emitting diode from the power line is determined according to a turn-on degree of the driving TFT such that the light emitting diode displays various gray levels. Since the storage capacitor maintains the voltage of the gate electrode of the driving TFT when the switching TFT is turned off, the level of the current flowing through the light emitting diode is maintained until a next frame even when the switching TFT is turned off
According to an emission direction of a light from the light emitting diode, the OLED display devices may be classified as top emission devices and bottom emission devices. Since an aperture ratio is reduced in the bottom emission OLED display device, the top emission OLED display device has been widely used.
In the top emission OLED display device, a semiconductor layer, a gate insulating layer, a gate electrode, an interlayer insulating layer and source and drain electrodes are sequentially formed on a first substrate to constitute the driving TFT. The source and drain electrodes are connected to the power line and the light emitting diode, respectively.
The light emitting diode includes first and second electrodes and an organic emitting layer between the first and second electrodes. The first electrode is connected to the driving TFT in each pixel region, and the second electrode is formed on an entire surface of the first substrate having the organic emitting layer. In addition, a second substrate facing the first substrate is formed on the second electrode for encapsulation.
The first electrode as an anode includes a material having a relatively high work function, and the second electrode as a cathode includes a material having a relatively low work function. For the top emission type, the second electrode of a top layer on the first substrate may have a transparent property with respect to visible light, and the first electrode under the second electrode may have a reflective property with respect to the visible light for improving light efficiency.
In general, since the material having the relatively low work function is an opaque metallic material, the second electrode of the opaque metallic material may be formed with a small thickness to have the transparent property. However, as the thickness of the second electrode decreases, a resistance of the second electrode increases and a base voltage drops to cause deterioration such as non-uniformity in luminance distribution.